The invention relates to a longitudinal plunging unit for torque transmitting purposes in a shaft assembly. The unit includes an outer profiled sleeve having circumferentially distributed, inner, longitudinally extending first ball grooves to be connected to a first attachment part, a profiled journal positioned inside the outer profiled sleeve and having circumferentially distributed, outer, longitudinally extending second ball grooves to be connected to a second attachment part, groups of balls arranged in pairs of first and second ball grooves, and a sleeve-shaped ball cage which is positioned in the annular space between the profiled sleeve and the profiled journal and which fixes the groups of balls in their respective positions relative to one another.
Such axial plunging units serve the transmission of torque in shaft assemblies which, when in operation, are subject to changes in length. These changes in length, in a motor vehicle, for example, are caused by movements of one of the attachment parts due to compression and rebound actions. To the extent that reference is made to shaft assemblies, it is also possible for the latter to be formed largely by the longitudinal plunging unit itself which is then directly connected to attachment pieces such as welded-on flanges and slipped-on hubs.
When a profiled sleeve is displaced relative to a profiled journal while under torque, the rolling movement of the balls in the inner and outer ball grooves is substantially free from any sliding friction, so that the balls and thus the ball cage with all the balls cover half the relative plunging distance between the two parts. This permits the change in length of the longitudinal plunging unit to be of a low-friction nature. At the ends of the plunging path, axial stops for the ball cage or for the balls have to be provided in the profiled sleeve or on the profiled journal. Under normal operating conditions, the ball cage should preferably not reach the axial stops, but it should be freely displaceable on the plunging path specified by the design, thus avoiding any sliding friction of the balls in the grooves.
Assemblies of this type are used in torque-transmitting shafts, especially driveshafts whichxe2x80x94for compensating for tolerances in the distance between the attachment parts during assembly and/or for compensating changes in the distances between the attachment parts, such as joints, in operationxe2x80x94require low-friction plunging conditions. When in operation and during the transmission of torque, such driveshafts suffer from a problem in that the inter-engaging portions of the profiled sleeve and of the profiled journal are, by necessity, subject to torsion in the regions of the ball grooves.
As a result of the torsional movements of the profiled sleeve and of the profiled journal during the transmission of torque, there can occur uneven load conditions at the balls in the different cross-sectional planes. This adversely affects smooth and easy movability and can lead to early failure. In order to avoid this, it is desirable for both parts to feature a high degree of stiffness.
It is therefore an object of the present invention to provide a longitudinal plunging unit of the foregoing type which combines a high degree of strength with a lightweight design.
The present invention provides a profiled sleeve comprising a material with a substantially uniform wall thickness with a maximum deviation in wall thickness of xc2x115%. The profiled sleeve, in the region adjoining the first ball grooves, towards the first attachment part, changes integrally into a first cylindrical projection and, in the region adjoining the first ball grooves, towards the second attachment part, changes integrally into a second cylindrical projection. The two cylindrical projections mentioned improve the dimensional stiffness of the profiled sleeve. During the production of the profiled sleeve, the two cylindrical projections can be produced particularly easily by being formed out of a tubular member. The first cylindrical projection at the attachment end can be connected in an easy way to an adjoining shaft tube, either via an abutting connection or by being inserted into or slid onto same. The second cylindrical projection at the insertion end, which second cylindrical projection points towards the attachment part of the profiled journal, can be designed as a seal and stop for the balls held in the cage. If the second cylindrical projection has a greater inner diameter than the cross-section of the ball grooves, it is capable of accommodating sealing and stopping means by means of a press fit.
According to a preferred embodiment, the inner diameter of the first cylindrical projection is greater than an enveloping circle around the balls held in a functionally accurate or operationally accurate way in the cage. This allows the ball cage with the balls to be inserted from the attachment end. A stopping mechanism for the cage can then optionally be inserted into the first cylindrical projection, so that the cage cannot be disconnected from the profiled journal inside the profiled sleeve.
The profiled journal is preferably produced in the form of a hollow journal, such as from a material with a substantially uniform wall thickness with a maximum deviation in wall thickness of xc2x115%. This measure permits the greatest savings in respect of weight and material at the profiled journal, which savings have so far not been possible. In a preferred embodiment, in the region adjoining the second ball grooves, towards the second attachment part, the profiled journal is produced so as to change integrally into a tubular cylindrical portion whose outer diameter substantially corresponds to an enveloping circle around the second profiled grooves.
The profiled sleeve, in the region of the first ball grooves, is preferably provided with a metal armouring which comprises a high wear strength and which, on its own, also comprises a uniform wall thickness.
Both the profiled journal and the profiled sleeve can be produced from a tube by way of deformation, and the profiled sleeve provided with an armouring can be produced from a tube provided with an armouring sleeve which is inserted with a press fit. A radial material pre-tension between the profiled sleeve and the armouring sleeve has a strength-increasing effect. Analogously, the profiled journal can be provided with an armouring in the region of the ball grooves, which armouring can comprise an armouring sleeve which is slid on to a tube and which, together with the tube, is deformed into the profiled journal.
Other advantages and features of the invention will also become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.